Bipolar II disorder and borderline personality disorder share several common symptoms, enough that differentiating between the two conditions is tricky. Both are mood disorders, meaning that the emotions are severe enough to create disruptions in daily living. Yet there are key differences between the two.

How Different are the Emotions From Normal?

One way to separate the two is to assess how different the emotional episode is from the person’s normal, or baseline, behavior. For example, a person with bipolar II experiences extreme emotional states. Sometimes the person lives with a manic high and sometimes with a depressive low. But these states are uncharacteristic of the person for long periods when they are asymptomatic. In other words, the person has a baseline personality that is quite separate from their mania or depression.

By contrast, the emotional state of the individual with borderline personality disorder is rather constant. The challenges the person faces because they have trouble interacting with others or responding appropriately are ever-present because they are part of their baseline personality.

How Variable Are the Emotions?

For diagnosis purposes the individual with bipolar II must experience at least a single manic episode, characterized by high energy, euphoria and high self-confidence among other things. The person may demonstrate impulsive behaviors, have trouble controlling their speech or engaging in high risk activities. When they are not in the midst of mania impulsivity is not a problem.

For the person with borderline personality disorder sadness, irritability, anxiety and emptiness are chronic states of being. The person with this disorder does not experience euphoria or a sense of grandiosity and, for them, controlling behavior is an ongoing problem.

How Often Do They Change?

The two conditions are separated not only by what kinds of emotions they experience, but also by how often those emotions change. The person with borderline personality disorder overreacts on a somewhat regular basis. Anxiety, anger and feeling blue are the drumbeat of life. At times, these feelings will burst forth in more dramatic ways, but it is often the case that the outburst is short-lived and can be traced to a single event or trigger, usually a perceived offense or a fear of being abandoned.

Bipolar, on the other hand, produces prolonged emotional swings that can last for days or weeks. While these episodes are present the person doesn’t seem like themselves. And, unlike borderline personality disorder, these emotional shifts are just as likely to occur without any kind of trigger.

How Do the Two Get Misdiagnosed?

If the disorders are so different, how is it that they are so often confused? The answer lies in the fact that bipolar II frequently produces extended episodes of depression. The depression is far more prevalent than are periods of mania or hypomania which may show up only occasionally. Because of this, the chronic sadness of a depressive episode can be mistaken for the more fixed despondency associated with borderline personality disorder.

The onset of bipolar and borderline often occur during adolescence, providing another confusing overlap. However, in the case of borderline the emotional and behavioral responses to life became part and parcel of the person’s typical mode of coping. Bipolar II disorder, as mentioned before, is not so much a matter of core personality as it is extreme shifts away from that center.

Because it can be tough to tease out the differences between these two conditions there is nothing wrong with seeking out a second opinion, or at least asking plenty of questions of the diagnosing clinician. The important dividing line will be in what variations, if any, take place from the person’s baseline behavior and personality.